The invention relates generally to the field of disposal of highly radioactive materials, and, more particularly, to a method and apparatus for reducing the volume of radioactive rectangular tubular fuel channels stored under water.
In one type of boiling water nuclear reactor (BWR), there is a fuel assembly consisting of fuel rods surrounded by a fuel channel. The channel is a 5.278 inch square tube, approximately fourteen feet long, with open ends and made of zircalloy. The channels typically have a wall thickness of 0.080, 0.100 or 0.120 inch.
There are a large number of these fuel assemblies in a BWR reactor, and one-third of these assemblies are normally replaced each year. Even though the fuel channels are normally reused after the fuel rods are removed, for various reasons it has been determined that in some cases, they cannot be resued, but must be replaced, thereby requiring these highly radioactive fuel channels to be disposed of in a safe and economical manner.
These used fuel channels are highly radioactive for two reasons. First, the zircalloy metal itself has become somewhat radioactive during operation of the nuclear reactor, and second, there is formed on the outside of the channel a crust or crud which itself is also highly radioactive.
The present method of disposing of such radioactive fuel channels is to place them in a special heavy metal shipping cask, and transport them to one of the five federal disposal grounds in the country where they are then buried. However, the rental for these casks is quite expensive, and it would be highly desirable to reduce the effective volume of these tubular fuel channels thereby to increase the number of channels which can be shipped in each cask.
There are presently hundreds of these fuel channels stored in water-filled fuel pools at numerous BWR-nuclear power plants. Due to the radiation levels of these fuel channels, they must be handled under water, thus posing one problem. Another problem is that the handling operation must result in as little debris as possible, since such debris is radioactive and will contaminate the pool water.
One suggestion has been to crush the fuel channels in order to reduce their volume, but this procedure would result in a great deal of debris in the form of flaked-off radioactive crust dislodged from the channel during the crushing operation. In addition, the volume reduction would not be optimum using this method of compaction.